Fuel cell system

ABSTRACT

An FC system disclosed herein comprise FC units, a cooler and a controller. Each of the FC units comprises a FC stack, a supply/a return/a circulating passages through which refrigerant flows and first to third temperature sensors. The first to third temperature sensors measure temperatures of the refrigerant in the passages at different positions. The controller is configured to stop a specific FC unit, compare measured values of the first to third temperature sensors of the stopped specific FC unit and, when one of the measured values differs from the other two of the measured values, provide notification about malfunction of the temperature sensor with the different measured value.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2021-198685, filed on Dec. 7, 2021. the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The technique disclosed herein relates to a fuel cell system including aplurality of fuel cell stacks.

BACKGROUND

For example, Japanese Patent Application Publication No. 2005-093349 andJapanese Patent Application Publication No. 2020-136205 each describe afuel cell system including a plurality of fuel cell stacks. Since thefuel cell stacks generate heat while they generate electricity, the fuelcell system includes a cooler which cools the plurality of fuel cellstacks. The fuel cell system of Japanese Patent Application PublicationNo. 2005-093349 includes one common cooler for the plurality of fuelcell stacks. Refrigerant supplied from the one cooler is distributed tothe plurality of fuel cell stacks. The fuel cell system of JapanesePatent Application Publication No. 2020-136205 includes the same numberof coolers as the fuel cell stacks, and each of the coolers cools itscorresponding fuel cell stack.

For clearer description, “fuel cell” will simply be hereafter referredto as “FC”. That is, “fuel cell system” will simply be referred to as“FC system”, “fuel cell unit” will be referred to as “FC unit”, and“fuel cell stack” will simply be referred to as “FC stack”.

SUMMARY

In order to maintain temperatures of FC stacks within a suitabletemperature range, a FC system includes temperature sensors eachconfigured to measure a temperature of refrigerant to be supplied to itscorresponding FC stack and a temperature of the refrigerant which passedthrough the FC stack. When the temperature sensors fail, the FC stackscannot suitably be cooled. The present disclosure relates to an FCsystem including a plurality of FC units (FC stacks) and provides atechnique for checking temperature sensors included in each of the FCunits.

An FC system disclosed herein may comprise a plurality of FC units, acooler and a controller. Each of the FC units may comprise a FC stack, asupply passage/a return passage/a circulating passage through whichrefrigerant flows and first to third temperature sensors. The supplypassage may supply the refrigerant from the cooler to the FC stack. Thereturn passage may return the refrigerant which passed through the FCstack to the cooler. The circulating passage may be connected to thesupply passage and the return passage. The first temperature sensor maybe configured to measure a temperature of the refrigerant in the supplypassage at a position upstream of a merging point of the supply passageand the circulating passage. The second temperature sensor may beconfigured to measure a temperature of the refrigerant in the supplypassage at a position downstream of the merging point. The thirdtemperature sensor may be configured to measure a temperature of therefrigerant in the return passage.

The controller may be configured to stop a specific FC unit among theplurality of the fuel cell units, and check the temperature sensors bythe following processes while operating the FC units other than thespecific FC unit so that a total output of the FC units other than thespecific FC unit matches a target output. In other words, the controllermay be configured to compare measured values of the first, second andthird temperature sensors of the stopped specific FC unit and, when oneof the measured values differs from the other two of the measuredvalues, provide notification about malfunction of the temperature sensorwith the different measured value. Here, “provide notification aboutmalfunction” means to send a signal indicating that the temperaturesensor of which measured value is different is malfunctioning to adifferent computer or a display device.

The FC system disclosed herein can check the temperature sensors whilerealizing the given target output. When one of the first and the secondtemperature sensors outputs the measured value different from themeasured values outputted from the other two temperature sensors, thecontroller may be configured to restart the specific FC unit which isstopped. In that case, the controller controls the operating FC units,including the restarted FC unit, so that the total output of the FCsystem matches the target output.

Details of the technique disclosed herein and further developments willbe described in “DETAILED DESCRIPTION”.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a block diagram of a fuel cell system of anembodiment;

FIG. 2 illustrates a flowchart of a temperature sensor check process;

FIG. 3 illustrates a flowchart of a first sub-process of FIG. 2 ; and

FIG. 4 illustrates a flowchart of a second sub-process of FIG. 2 .

DETAILED DESCRIPTION

With reference to figures, an FC system 2 of an embodiment will bedescribed. As described above. “FC” is a simpler term of a fuel cell.FIG. 1 illustrates a block diagram of the FC system 2. A controller 7and respective devices (FC stacks 11, step-up converters 12, pumps 24,switch valves 25, temperature sensors 31 to 33) are connected to oneanother via communication lines, however, illustration of thecommunication lines is omitted.

The FC system 2 is a power source which generates electricity using thethree FC stacks 11, and is configured to supply electric power to adifferent device from a system output terminal 3.

The FC system 2 includes the three FC units 10 a to 10 c, a cooler 4,and a controller 7. The three FC units 10 a to 10 e have the samestructures. The three FC units 10 a to 10 c may be referred to as FCunits 10 when they are described without distinction therebetween.

Each of the FC units 10 includes a FC stack 11 and a refrigerant circuit20. Each of the FC stacks 11 is configured to generate electricity. Ineach of the FC units 10, the refrigerant circuit 20 receives a coolrefrigerant from the cooler 4 and cools the FC stack 11. The refrigerantcircuit 20 returns the refrigerant that passed through the FC stack 11to the cooler 4. The cooler 4 is a radiator configured to release heatof the refrigerant to air.

The step-up converter 12 accompanies each of the FC stacks 11. Thestep-up converter 12 is connected to a power output terminal of the FCstack 11, and an output terminal of the step-up converter 12 isconnected to the system output terminal 3. The step-up converter 12 isconfigured to step up direct current generated by the FC stack 11 andsupply the same to the system output terminal 3. The electricitygenerated by the plurality of FC stacks 11 is suppled from the systemoutput terminal 3 to a different device. Even when output voltages ofthe plurality of FC stacks 11 are different, outputs of the plurality ofFC stacks 11 can he summed and outputted from the system output terminal3 by equalizing output voltages of the step-up converters 12. Whenelectric power is supplied to a device driven by alternating currents,an inverter is connected between the device and the system outputterminal 3.

In each of the FC stacks 11, fuel gas (hydrogen gas) and air (oxygen)react, by which electricity is generated. The controller 7 controlsamounts of fuel gas and air to be supplied to each of the FC stacks 11,by which desired electricity can be obtained. Illustration of device(s)for supplying fuel gas and air to each of the FC stacks 11 is omitted.

A temperature of each of the FC stacks 11 rises during generation ofelectricity. The FC system 2 includes the same number of refrigerantcircuits 20 as the FC stacks 11, and each of the refrigerant circuits 20can separately cool its corresponding FC stack 11.

Although the FC system 2 includes the plurality of refrigerant circuits20 (plurality of FC units 10 a to 10 c), the plurality of refrigerantcircuits 20 shares one cooler 4. A common supply passage 5 and a commonreturn passage 6 are connected to the cooler 4. The common supplypassage 5 supplies the refrigerant to the plurality of refrigerantcircuits 20 and the common return passage 6 returns the refrigerantflown out of the plurality of refrigerant circuits 20 (refrigerant whichpassed through the FC stacks 11) to the cooler 4.

The plurality of FC units 10 has the refrigerant circuits 20 having thesame structure as one another. Each of the refrigerant circuits 20includes a supply passage 21, a return passage 22, a circulating passage23, a pump 24, a switch valve 25, a fluid joint 26, and temperaturesensors 31 to 33. The supply passage 21 supplies the refrigerant to itscorresponding FC stack 11 from the cooler 4. The return passage 22returns the refrigerant that passed through the FC stack 11 to thecooler 4. The supply passage 21 communicates with the cooler 4 via thecommon supply passage 5, and the return passage 22 communicates with thecooler 4 via the common return passage 6. As described above, heat ofthe refrigerant that passed through the FC stack 11 is released at thecooler 4 to the air, and then the refrigerant is supplied to the FCstack 11 again.

The circulating passage 23 is connected to the supply passage 21 and thereturn passage 22. The circulating passage 23 returns the refrigerant inthe return passage 22 (refrigerant that passed through the FC stack 11)to the supply passage 21. The switch valve 25 is disposed at aconnecting point of the circulating passage 23 and the return passage22. The switch valve 25 is configured to set a destination of therefrigerant flowing in the return passage 22 to one of the cooler 4 andthe circulating passage 23. The switch valve 25 is controlled by thecontroller 7. The circulating passage 23 and the supply passage 21 arecoupled by the fluid joint 26.

The pump 24 is disposed on the supply passage 21. The pump 24 isconfigured to pump the refrigerant to the FC stack 11. The controller 7controls the pump 24. By adjustment of an output of the pump 24, a flowrate of the refrigerant supplied to the FC stack 11 (i.e., coolingperformance) can be adjusted.

Two temperature sensors (a first temperature 31 and a second temperaturesensor 32) are disposed on the supply passage 21. The first temperaturesensor 31 is disposed at a position upstream of a merging point (fluidjoint 26) of the circulating passage 23 and the supply passage 21, andthe second temperature sensor 32 is disposed at a position downstream ofthe merging point (fluid joint 26). In other words, the firsttemperature sensor 31 is disposed on the supply passage 21 between themerging point (fluid joint 26) and the cooler 4, and the secondtemperature sensor 32 is disposed on the supply passage 21 between themerging point (fluid joint 26) and the FC stack 11. The firsttemperature sensor 31 is configured to measure a temperature of therefrigerant supplied from the cooler 4. The second temperature sensor 32is configured to measure a temperature of the refrigerant flowing intothe FC stack 11. The merging point (fluid joint 26) is positionedbetween the first temperature sensor 31 and the second temperaturesensor 32. When the refrigerant that passed through the FC stack 11flows through the circulating passage 23 into the supply passage 21,measured values of the first temperature sensor 31 and the secondtemperature sensor 32 may be different.

The third temperature sensor 33 is disposed on the return passage 22.The third temperature sensor 33 is configured to measure a temperatureof the refrigerant flowing in the return passage 22 (i.e., temperatureof the refrigerant that passed through the FC stack 11). A measuredvalue of the third temperature sensor 33 is dealt as an approximationvalue of the temperature of the FC stack 11.

The controller 7 adjusts an output of the pump 24 so that the measuredvalue of the third temperature sensor 33 (approximation temperature ofthe FC stack 11) is within a predetermined allowable temperature range.When the measured value of the second temperature sensor 32 (temperatureof the refrigerant flowing into the FC stack 11) is low, the controller7 controls the switch valve 25 and sets the destination of therefrigerant in the return passage 22 to the circulating passage 23 sothat the refrigerant that passed through the FC stack 11 returns to theFC stack 11. By returning the refrigerant that passed through the FCstack 11 again to the FC stack 11, drastic decrease in the temperatureof the FC stack 11 can be prevented.

As described above, the three FC units 10 a to 10 c have the samestructure, thus explanations for the other FC units 10 b, 10 c areomitted.

The controller 7 of the FC system 2 periodically checks if thetemperature sensors 31 to 33 of each of the FC units 10 are operatingnormally. A display 8 and a host controller 9 are connected to thecontroller 7. When any of the temperature sensors malfunction, thecontroller 7 sends a signal providing notification about malfunction ofthe temperature sensor to the display 8 and the host controller 9.

With reference to FIG. 2 and FIG. 3 , a temperature sensor check processperformed by the controller 7 will be explained. The controller 7periodically performs the process of FIGS. 2 and 3 while at least one ofthe FC stacks 11 generates electricity. Even while the temperaturesensor check process is performed, the controller 7 adjusts the outputof the pump 24 of each of the operating FC unit(s) 10 so that atemperature of each of the FC stack(s) 11 (measured value of thecorresponding third temperature sensor 33) is within the predeterminedallowable temperature range. A target output of the FC system 2 isexternally given to the controller 7. The controller 7 operates theplurality of FC units 10 to meet the target output.

Firstly, the controller 7 temporarily stops a specific FC unit 10 (stepS12). At this time, the controller 7 operates the (available) FC units10 other than the specific FC unit to meet a target output given to theFC system 2. “Temporarily stops the FC unit” refers to a state in whichsupply of fuel gas and air is stopped but the FC unit can restart at anymoment. For example, the controller 7 closes a valve (fuel valve) on apipe for supplying fuel gas to the FC stack 11 and a valve (air valve)on a pipe for supplying air to the FC stack 11, hut leave the otherauxiliary devices activated. The “auxiliary devices” herein refer todevices related to operation of the FC stack 11.

Next, the controller 7 controls the switch valve 25 so that therefrigerant does not flow to the circulating passage 23 (step S13). Thecontroller 7 controls the switch valve 25 so that the refrigerant in thereturn passage 22 (the refrigerant that passed though the FC stack 11)flows into the cooler 4. The controller 7 simultaneously drives the pump24 which pumps the refrigerant to the FC stack 11 (step S13). The FCstack 11 that is temporarily stopped is not generating electricity, butthe FC stack 11 is rapidly cooled by supplying the refrigerant to the FCstack 11.

Since the FC stack 11 is rapidly cooled, a temperature of therefrigerant flowing into the FC stack 11 and a temperature of therefrigerant flowing out of the FC stack 11 become equal. Since therefrigerant does not flow into the circulating passage 23, a temperatureof the refrigerant is also equal at positions downstream and upstream ofthe fluid joint 26.

The controller 7 compares measured values of the first to thirdtemperature sensors 31 to 33 (step S14). When the measured values of allthe temperature sensors match, it can be determined that the all thetemperature sensors operate normally. “Measured values match” means thata difference among the measured values is within a predetermineddifference.

When the measured values of the second temperature sensor 32 and thethird temperature sensor 33 match but the measured value of the firsttemperature sensor 31 does not match the measured value of the secondtemperature sensor 32 (or the third temperature sensor 33), thecontroller 7 determines that the first temperature sensor 31 ismalfunctioning. “Measured values do not match” means that the differencebetween the measured values exceeds the predetermined difference.

When the measured values of the first temperature sensor 31 and thethird temperature sensor 33 match but the measured value of the secondtemperature sensor 32 does not match the measured value of the firsttemperature sensor 31 (or the third temperature sensor 33), thecontroller 7 determines that the second temperature sensor 32 ismalfunctioning. When the measured values of the first temperature sensor31 and the second temperature sensor 32 match but the measured value ofthe third temperature sensor 33 does not match the measured value of thefirst temperature sensor 31 (or the second temperature sensor 32), thecontroller 7 determines that the third temperature sensor 33 ismalfunctioning.

When all the temperature sensors operate normally (the temperaturesensors are not malfunctioning), the controller 7 restarts the FC unitthat is temperately stopped (step S15). When the first temperaturesensor 31 or the second temperature sensor 32 malfunctions, thecontroller 7 performs a first sub-process (step S16). When the thirdtemperature sensor 33 malfunctions, the controller 7 performs a secondsub-process (step S17).

FIG. 3 illustrates the first sub-process. When the first temperaturesensor 31 malfunctions, the controller 7 provides notification aboutmalfunction of the first temperature sensor 31 (step S22). Here,“provide notification about malfunction” means to send a signalindicating that the temperature sensor is malfunctioning to the uppercontroller 9 or the display 8. When the second temperature sensor 32malfunctions as well, the controller 7 provides notification aboutmalfunction of the second temperature sensor 32 (step S22).

When the first temperature sensor 31 or the second temperature sensor 32malfunctions, the controller 7 re-starts the FC unit 10 that istemporarily stopped (step S23). At this point, the third temperaturesensor 33 operates normally. As described above, the measured value ofthe third temperature sensor 33 shows an approximation value of thetemperature of the FC stack 11. As long as the third temperature sensor33 operates normally, the temperature of the FC stack 11 can bemaintained within a tolerable temperature range even when the firsttemperature sensor 31 or the second temperature sensor 32 malfunctions.

However, when the first temperature sensor 31 or the second temperaturesensor 32 malfunctions, this may cause a problem in the followingsituation. In other words, the controller 7 cannot recognize thetemperature of the refrigerant supplied from the cooler 4 (when thefirst temperature sensor 31 malfunctions). Alternatively, when therefrigerant that passed through the FC stack 11 is flown into thecirculating passage 23, the controller 7 cannot recognize thetemperature of the refrigerant flowing into the FC stack 11 (when thesecond temperature sensor 32 malfunctions). In these cases, thecontroller 7 cannot promptly or accurately control the temperature ofthe FC stack 11. In this case, the controller 7 limits a maximum outputof the FC stack 11 to avoid abrupt change in the temperature of the FCstack 11. With such a process, even when the first temperature sensor 31or the second temperature sensor 32 malfunctions, the controller 7 canmaintain the temperature of the FC stack 11 within the tolerabletemperature range based on the measured value of the third temperaturesensor 33. After step S23 is performed, the process of the controller 7shifts to step S18 of FIG. 2 .

FIG. 4 illustrates a flowchart of a second sub-process. When the thirdtemperature sensor 33 malfunctions, the controller 7 providesnotification about malfunction of the third temperature sensor 33 (stepS32). The meaning of “provide notification about malfunction” in stepS32 is the same as the meaning of “provide notification aboutmalfunction” in step S22.

Next, the controller 7 closes the FC unit 10 which is temporarilystopped (step S33). Here, “closes the FC unit 10” means to stop all theauxiliary devices related to operation of the FC unit 10, including thepump 24. The valve on the pipe for supplying fuel gas and valve on thepipe for supplying air to the FC unit 10 remain closed. When the thirdtemperature sensor 33 malfunctions, the controller 7 cannot recognizethe temperature of the FC unit 10, thus the FC unit 10 of which thirdtemperature sensor 33 has failed is not used until the third temperaturesensor 33 is fixed. After step S33 is performed, the process by thecontroller 7 shifts to step S18 of FIG. 2 .

The controller 7 performs the temperature sensor check process for allthe FC units 10 (step S18: NO). When the temperature sensor checkprocess is performed for all the FC units 10, the temperature sensorcheck process terminates (step S18: YES). When the temperature sensorcheck process terminates. the controller 7 controls the available FCunits 10 so that the target output given to the FC system 2 is met.

As described above, the FC system 2 can check the temperature sensorswhile meeting the target output.

Characteristics of the FC system 2 of the embodiment will be listedbelow. The FC system 2 comprises: the plurality of FC units 10 a to 10c; the cooler 4 (radiator); the first to third temperature sensors 31 to33, and the controller 7. Each of the FC units 10 comprises: the FCstack 11; the supply passage 21, the return passage 22, the circulatingpassage 23, the switch valve 25, and the pump 24. The supply passage 21supplies the refrigerant from the cooler 4 to the FC stack 11. Thereturn passage 22 returns the refrigerant which passed through the FCstack 11 to the cooler 4. The circulating passage 23 is connected to thesupply passage 21 and the return passage 23. The refrigerant in thereturn passage 22 is returned to the supply passage 21 through thecirculating passage 23. The switch valve 25 is configured to set thedestination of the refrigerant flowing in the return passage 22 to oneof the cooler 4 and the supply passage 21. The first temperature sensor31 is configured to measure a temperature of the refrigerant in thesupply passage 21 at a position upstream of the merging point (fluidjoint 26) of the supply passage 21 and the circulating passage 23. Thesecond temperature sensor 32 is configured to measure a temperature ofthe refrigerant in the supply passage 21 at a position downstream of themerging point. The third temperature sensor 33 is configured to measurea temperature of the refrigerant in the return passage 22. Thecontroller 7 is configured to: stop the specific FC unit 10 and operatethe (available) FC units 10 other than the specific FC unit 10 so that atotal output of the FC system 2 matches the target output. Thecontroller 7 compares the measured values of the first temperaturesensor 31, the second temperature sensor 32 and the third temperaturesensor 33 of the specific FC unit 10. When one of the three measuredvalues is different from the other two measured values, the controller 7provides notification about malfunction of the temperature sensor ofwhich measured value if different.

Notes regarding the technique described in the embodiment will bedescribed. The FC system disclosed herein may include four or more FCunits of which power output terminals are connected in parallel.Alternatively, the FC system disclosed herein may be of type includingtwo FC units of which power output terminals are connected in parallel.

While specific examples of the present disclosure have been describedabove in detail, these examples are merely illustrative and place nolimitation on the scope of the patent claims. The technology describedin the patent claims also encompasses various changes and modificationsto the specific examples described above. The technical elementsexplained in the present description or drawings provide technicalutility either independently or through various combinations. Further,the purpose of the examples illustrated by the present description ordrawings is to satisfy multiple objectives simultaneously, andsatisfying any one of those objectives gives technical utility to thepresent disclosure.

What is claimed is:
 1. A fuel cell system comprising: a plurality offuel cell units; a cooler; and a controller, wherein each of theplurality of the fuel cell units comprises: a fuel cell stack; a supplypassage for supplying refrigerant from the cooler to the fuel cellstack; a return passage for returning the refrigerant which passedthrough the fuel cell stack to the cooler; a circulating passageconnected to the supply passage and the return passage; a firsttemperature sensor configured to measure a temperature of therefrigerant in the supply passage at a position upstream of a mergingpoint of the supply passage and the circulating passage; a secondtemperature sensor configured to measure a temperature of therefrigerant in the supply passage at a position downstream of themerging point; and a third temperature sensor configured to measure atemperature of the refrigerant in the return passage, the controller isconfigured to: stop a specific fuel cell unit among the plurality of thefuel cell units; operate the fuel cell units other than the specificfuel cell unit so that a total output of the fuel cell system matches atarget output; and compare measured values of the first, second andthird temperature sensors: and when one of the measured values differfrom the other two of the measured values, provide notification aboutmalfunction of the temperature sensor with the different measured value.2. The fuel cell system of claim 1, wherein when one of the first andthe second temperature sensors outputs the measured value different fromthe measured values outputted from the other two temperature sensors,the controller is configured to restart the specific fuel cell unit.